Quote Originally Posted by thebigspendur View Post
What does tensile strength have to do with shaving? You're not pulling the hairs out. It's the hardness of the hair that matters as the blade cuts through them.

As far as prep goes I start with a clean face. The shave soap provides all that is necessary for a great shave. My experience of course.
A razor blade is one of the most basic of tools, a simple wedge. When you shave the apex of the wedge starts to penetrate the hair and then the wedge shape pushes the keratin molecules apart until the tensile strength of the keratin chains can no longer sustain the force applied by the wedge. At that point, the hair is severed. Thus, the tensile strength of the hair is very important. Keratin molecules have very little strength in compression, but have good tensile strength.

Remember that tensile strength also depends upon the diameter of the "wire". Fine hair has a smaller diameter and thus a lower tensile strength than coarse hair. Thus, the coarser your hair, the more critical facial preparation becomes.